Apparatus for control of roof location in the formation of underground caverns by solution mining



c. T. BRANDT 2,772,868 APPARATUS FOR CONTROL OF ROOF LOCATION IN THE Dec. 4, 1956j FORMATION OF UNDERGROUND CAVERNS BY SOLUTION MINING Filed Jan 18, 1954 INVENTOR.

\ CTBRANDT By MM. Y

ATTORNEYS LEVEL CONTROL PIPE COMPRESSOR SALT Y WATER' APPARATUS FOR CONTROL OF ROOF LOCATION IN THE FORMATION OF UNDERGROUND CAV- ERNS BY SOLUTION MINING Carl T, Brandt, Bartlesville, Okla., assignorto Phillips This invention relates to an improvement in the means for mining a soluble material, such asrock salt, with a solvent. This invention relates to that class of mining in which a solvent, `such as water, is introduced into a well drilled into a formation of salt and the resulting solution containing salt is discharged from the said well, and in which a non-solvent, such as air, is introduced into the well to forma protective layer betweenthe solvent and the roof of the forming cavity. In one of its more specic aspects, this invention relates to an` improved means for preparing an underground `storage cavern in a soluble formation.

In recent years, a great deal of consideration has been given to the problem of storage of lmaterials which, for economic reasons, are produced on` a year-round basis, but which have heavy seasonal consumption rates. That is, large volume storage facilities are required. This problem is being solved, in the case of liquids or easily liqueable materials, by means of underground s torage Caverns formed in salt formation.

A method now in use, in forming underground storage caverns, for dissolving salts by means of wells drilled through the bed, requires the circulation ofjliquid solvent through casings either to the top or bottom of the opening. If the liquid is introduced at the top of the bed, it oats on the heavier salt laden solution and-continues to attack the salt near the top of the opening. As this fresh solven dissolves salt, it sinks and is replaced so that freshlsolvent is always near the'surface.` `Even when the solvent is introduced near the bottom of the bed, it will rise through the heavy salt laden solution' to liattented Dec. 4, 1956 ICC outer casing previously described, then only a minimum of non-recoverable storage is created.

A seriousrdisadvantage of the present systems is that the non-solvent is introduced under pressure and its total volume, Where the non-solvent is a gasrsuch as air, is dependent upon pressure and temperature relationships. To adjust the non-solvent level, it has been necessary to either regulate pressure or change the length of the protective casing which requires the use of heavy equipment at considerable expense. I have found that the solvent level, and consequently the protected depth, can be easily andreadily maintained or changed, as desired, by the use of a smalldiameter vent pipe communicating fromlthe desired solvent levelto the earths surface.l The solvent level can be changed by simply raising or lowering the vent pipe or level control pipe.

An object of this invention is, therefore, to provide a means for regulating the solvent level in underground mining of a salt when injecting a solvent into a well drilled into the salt and ushing the resulting solution from the resulting cavity. A further object of my invention is to provide a means for controlling the cavity shape the top of the opening. In either case, thechief'. point of attack on the salt 'is near the surface of the solvent. The undesirable tendency of the chamber to coneiwith resultant over development ofthe roof can be minimized if the distance between thetop and bottomof the chamber in which dissolving is taking place is heldto a minimum. Whenv this distance is held to a minimum, the chamber tends to take the shape of thev much. `more desirable frustum of a cone. q.

In order to control the height ofthe chamber inV which dissolving is taking place, a non-solvent uid, such as air, is introduced into the cavern. This Huid, having adensity less than the solvent, floats on the solvent and protects the roof and upper side of the cavern from attack by the solvent. As a result, the roof heighth `is held constant ber. l

When this portion of the cavern reaches the desired diameter, the non-solvent is removed thereby exposing the roof to dissolution. The dissolving of the roof can proceed until the desired thickness has been removed, at which time, the non-solvent is again introduced and roof dissolution stopped. Since the, bottom has already been dissolved out,by controlling the thickness ofthe roof, we are actually holding the. distancebetweenV ,the

top and the bottom vof the chamber to a' `minimum and k l 4forcing the chamber to take the 'shape ofa frustur'n; By

and all dissolvlng takes place below the top of the cham- N l string is to Pfote-:ct the permanent 4casing Seat. However and roof location in preparing a cavern in a salt formation by means of a solvent. A still further object of my invention is to provide a means for preparing an underground storage cavern of the desired size and shape formed in a rock salt bed.

In discussing this invention, I will use as an illustration, ,the formation of an underground storage'cavern in a bed of rock salt. I will use water as the solvent and air as the non-solvent. It will be seen by those skilled in the art that my invention is equally applicable to underground cavern forming `in any` soluble material deposited in underground beds. Water and air are the most abundant and cheapest materials available for the respective purpose of solvent and non-solvent, however, other materials can be used, if desired.

It has been the general practice in the formation of underground caverns in salt formation by dissolving to first `drill a well from the surface to a position in the formation approximating the desired location in the top of the cavern. Apermanent casing between the surface and the salt formation is then set and cemented in place, the cement making a tight seal. The hole is then drilled through the permanent casing down to a position approximating the desired location of the bottom of the cavern. A protective string is then placed inside the 4permanent casing and lowered` to well below the seat of the permanent casing. AV wash string is then placed inside theprotective stringandprojects below the protective string to a position closely spaced to the bottom of the Well. f In normal operation, water is put into the well through the wash string, and brine is removed through theannular space between the wash and protectivestrings, however, the wash direction can be reversed..

Theoretically, one of the functions of the protective due to factors previously discussed, this has not been true, the fresh solvents on top dissolving the saltseat away. i According to invention, la compressoris tied into the 'annular space,V between the permanent casing and the protective string'and into the fresh water supply line (wash string). An open end small diameterv pipe is in- Vserted through theannular space between the permanent string andthe lprotective string and is lowered to the desired Water Vlevel and the upper end `is open to the atmosphere.l The bottomV of Athe open end pipe, of

course, must be above the-brine outlet string. This small i open end pipe is called the level control pipe.

The fresh water line is opened and the well is filled. With the well full of water, the compressor is started. As pressure builds up, the level of the water will be forced downward and the displaced water will move out through the brine discharge line. The water will continue to be forced downward until the bottom Vof the level control pipe is open to air and the excess air is released to the atmosphere. As the pressure is thus released, the Water will again rise, closing oif the level control pipe and the cycle is repeated.

I have found that very close control of the liquid level in underground mining can be maintained by the use of my apparatus. When the liquid level is forced down below the bottom of the level control pipe, the air escaping acts as an air lift and pushes brine ahead of it as it escapes. For that reason, it is desirable to use a small diameter pipe so as to keep the volume of brine low and to use a small volume of air, thereby minimizing the amount of blow off. For these reasons, I prefer as my level control pipe a conduit of less thanone inch (1") diameter and have found that a standard 1/2" diameter pipe gives excellent results. I have also found that an air rate from 1A to 1 cubic foot per minute (standard conditions) is suicient even in relatively large diameter caverns, say up to 50 feet. In general, these caverns will not be so large since diameters greater than 20-35 feet may cave in from the roof. Of course, the maximum diameter will depend upon the particular formation and the factors determining this are outside the scope of this invention. However, once this has been determined, my invention is useful in controlling the diameter in the desired range.

I will further describe my invention by referring'to the attached drawing which is a diagrammatic vertical section showing my invention in a typical cavern forming operation.

I will describe a typical installation used for .preparing an underground cavern in a rock salt bed for underground storage. I will use water as my solvent and air as my non-solvent, since these materials are usually readily available in large quantities and at low cost. The dimensions used are typical but are not limiting.

Referring to the drawing, a well 1 is drilled from the earths surface 2 into the salt 3 to a position near the desired cavern bottom. A 13%" O. D. permanent casing 4 extends from the earths surface to shoulder 5 within the rock salt bed. This casing is sealed iluid tight by cement 6. This casing will remain in place after the cavern is formed and will serve as an accessV conduit for the underground storage equipment to be later installed. This permanent casing is capped by flange 6a. An 8%" O. D. protective string 7 passes through flange 6a and is centrally located within the protective casing and projects into the Well, generally below the highest desired liquid level. This protective nent casing by means of 1" conduit 14. A 1/2 conduit 15 connects conduit 14 with protective string 7.

In the operation of this embodiment, fresh water flows through the fresh water conduit 10 to the protective string 7 and into the well 1. This water dissolves salt 3 and the more concentrated solution settles to the bottom of the well and is forced out through the tubing (9). The compressor 13 is started and air flows through conduit 14 to annular space between the permanent casing 4 and the protective string 7. Air also llows through conduits 14 and 15 to the protective string 7 where it mixesl with fresh water. The pressure will build up in the cavern, forcing brine up through wash string 9 and conduit 11 to the brine pit. As has been hereinbefore indicated, the air pressure will continue to-build up, forcing the liquid level down to the bottom of the liquid level control pipe when the air will escape, releasing the pressure. The reduction in pressure will allow the liquid to rise and close otf Vthe bottom of the pipe. This in turn will cause a buildup of pressure and another lowering of the water level repeated and thereby maintain the liquid level. A

As has been hereinbefore said, the fresh solvent'will tend to'stay in the upper part of the liquid phase and being less concentrated will dissolve the salt at a more rapid'rate than will the more concentrated solution in the lower strata. As a consequence, the well will take on the appearance of a frustrum of a cone. When the base of the cone (upper level) reaches the desired diameter, the packing gland sealing the liquid level control pipe is loosened and the pipe is raised after which the gland is tightened and the pipe is again sealed. Then the procedure for admitting air and water as described above is repeated. This procedure is continued until the entire cavity is formed.

Air admitted to the fresh water is partially dissolved therein and is carried by this fresh water to all portions of the cavern. As this water dissolves salt, the air is released and will displace water in spaces such as space 16 behind bridges such as bridge 17.

. I have described my invention in one of its preferred embodiments. Those skilled in the art will see many modifications which can be made without departing from the scope of this invention. I have described my invention wherein an underground storage cavern is prepared in a rock salt bed. My invention is equally applicable for forming caverns in other soluble deposits.

v Other solvents may be employed, for example, hydrostring is sealed to flange 6a and is in turn capped by flange 8. A 41/2" O. D. wash string 9 passes through and is sealed to flange 8. This wash string is centrally located in the protective string and projects below the protective string to a position approximating the desired level of the cavern door. A fresh water conduit 10 is tied into the protective string. The wash string is connected to a brine conduit 11 which leads to a brine pit, not shown.

A standard 1/2 pipe 12 passes throughilange 6a and is located in the annular space between the protective string and the permanent casing. This 1/2 level control pipe projects downward to a position equal to the desired liquid level within the well. The upper end of this pipe is open to the atmosphere. This level .control pipe is sealed, generally by means of packing gland-,tothe flange 6a. A compressor 13, is connected to fthe permal carbon, ammonia or alcohol, depending upon the particular soluble material. Non-solvents other than air can be employed, for example, waste gases can be used as non-solvents for rock salt. The liquid level control pipe shown as being open to the atmosphere. If it is undesirable to exhaust the non-solvent to the atmosphere, this pipe can be connected to a collection vessel. If it i's undesirable to spray the brine Vof other solvents to the atmosphere, a liquid trap can be placed in the liquid level control pipe and the liquid removed can be conducted to the brine pit.

I claim:

l. An apparatus for underground mining of a soluble material by means of a liquid solvent said apparatus comprising in combination means for introducing solvent into `an underground bed of said soluble material, means for withdrawing solvent having soluble material dissolved therein from said bed, means for introducing a non-solvent lighter than said solvent and non-miscible therewith to top of said solvent introducedto said bed, and an open conduit communicating from the desired solvent level in said bed to the atmosphere Iabove the surface of the earth, said conduit being adjustable vertically. 2. An apparatus for controlling the cavern shape and roof location in underground mining of a soluble material by means of a liquid solvent saidV apparatus comprising in combination means for introducing solvent into an underground bed of said soluble material, means for withdrawing solvent having soluble material dissolved therein from said bed, means for introducing a nonsolvent gas into the cavity formed in said bed by said solvent and a vertically adjustable conduit of relatively small diameter adjustably disposed so as to communicate between the `desired liquid solvent level and the atmosphere above the earths surface.

3. The apparatus of claim 2 wherein the inside diameter of the vertically adjustable conduit is less than one inch.

4, The apparatus of claim 3, wherein the diameter of the adjustable conduit is within the range of one-quarter (1A) to one (l) inch.

5. An apparatus for underground mining of a salt deposited in underground beds by passing a solvent into and out of the said salt bed, thereby dissolving the salt and wherein a non-solvent of lesser density than t-he solvent is continuously passed into the cavity resulting from dissolving the salt, the apparatus comprising in combination a permanent casing extending from the salt bed to the earths surface and being cemented iluid tight into place, the permanent casing having a uid tight cap at its upper end; a protective string of smaller diameter than the permanent casing passing through the permanent casing cap and projecting below the bottom of the permanent casing into the salt bed, the protective string being so disposed as to have a common vertical axis with the permanent casing and thereby providing for an annular space between the protective string and the permanent casing; a liuid tight cap axed to the upper end of the said protective string; a wash string of lesser diameter than the protective string passing through the cap of the protective string and projecting below the bottom of the protective string into the salt bed to a position approximating the desired level of the cavity floor, the said wash string having a common vertical axis with the protective string and thereby providing for an annular space between the wash string and the protective string; means for admitting fresh solvent to the annular space between the wash string and the protective string; conduit means for removing solution from the upper end of the wash string; a vertically adjustable conduit having an inside diameter of less than one inch communicating from the desired solvent level to the atmosphere; the said adjustable conduit passing through the permanent casing cap and the annular space between the permanent casing and the protective string; pumping means for a non-solvent; a conduit means connecting the outlet of the said pumping means and the annular space between the permanent casing and the protective string; and conduit means connecting the last said conduit means and the annular space between said protective string and said wash string.

6. The apparatus of claim 5, wherein the salt is rock salt, the solvent is water, the non-solvent is air, and the adjustable conduit has a diameter in the range of onequarter (1A) to one (l) inch.

References Cited in the le of this patent UNITED STATES PATENTS 1,923,896 VTrump Aug. 22, 1933 2,009,534 Trump .4.--- July 30, 1935 2,618,475 Butler Nov. 18, 1952 

